In the Vesper Linder World, there aren't just Planes of Existence, but Dimensions and Time to travel through and experience as well.
Planes are basically mere copies of Dimensions. It depends on how far the Dimension has traveled, as per its rotation in the Multiverse and how 'close' the Dimesion is to the Material Dimesion or Plane.
Unlike our planet on Earth, rifts of the Multiverse move and exist all through Linderen. That means actual 'mini black holes ' actually move tbroughout the world like creatures would and do.
Travelling through a black hole is different from that of planer travel which is done through a wormhole.
Black holes are sucking in a certain amount of matter, to spit out another Universe on the other side in a big bang. The only way to travel through a black hole without dying since all of them filter matter down to the atomic level, but by bit, is with Sorcery. Without magic, one would die travelling to another Universe or the start of one.
Even if someone could get to the other side of a black hole, it would be Billions of years before any Intelligent life showed up in the cosmological clock of that Universe, since when entering the hole, one is always experience the time of that Realtys creation. Thus, a spell with years of wizardry is the only way to effectively speed up time and be able to reassemble you on the other.
Survivors of such a predicament have long told the tale of being caught floating in a vacuum of nothingness, then catapulted out of that magical error into any number of states. Monsters, demons, and many a creature have been mutated or spit out of that realm with the surviving adventurer.
And some often dont get reassembled correctly even without mutation losing whole limbs or just catching the deformity of traveling through time with cheaper or ineffective magic implements.
One thing is true of all black hole and time travelers: they all have added something to themselves in their travels. Memories that are not theirs, perhaps even the memories of Stars and Galaxies. Certainly the memories of the dead here who are the living in another realm, have been known to stay in the heads of those who dare to pass through.
The more common form of time and inter dimensional travel, is by use of the echoes of Dimensions: planes. Planes, as stated, are copies or parts of dimensions that do not require traveling through a black hole. In fact much of Linderen naturally shifts people through planes as anyone would travel through space in the Material realm. It also does not more often even require magic as planes are a natural part of the world itself.